Re: recurrence/proof help please


"Karl-Olav Nyberg" <konyberg@xxxxxxxxx> skrev i melding
news:d3e5pu$5el$1@xxxxxxxxxxxxxxxxx
>
> "jimbo" <jared.hodak@xxxxxxxxx> skrev i melding
> news:1113228464.518313.57130@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
>>I am in the process of solving a recurrence in a proof and I've hit a
>> snag. I currently have:
>>
>> the summation of ((N-L+1)(L-1)) from L=2 to N.
>>
>> I need to reduce this to something like
>>
>> the summation of ((NL-L^2)) from L=1 to N-1.
>>
>> but I can't quite figure out how to get there.
>>
>> Anyone have any ideas?
>>
>> Thanks.
>>
>
> Set L=L+1
>
> KON
>
OK. This was perhaps confusing.
Let L=S+1, then S=L-1 and S goes from 1 to N-1 (L=2 gives S=1, L=N gives
S=N-1)
Inserting L=S+1 into the summation gives
(NS-S^2) from S=1 to N-1.
You can now rename S to L and get (NL-L^2) from L=1 to N-1.

KON


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